Automatic switches for pumps which operate by sensing a predetermined value of a particular liquid parameter are known in the prior art. Pressure sensing switches for electric pumps are available in the marketplace. A pressure switch senses a single pressure source and opens or closes a single electrical circuit by means of one snap action electric switch. Pressure difference switches sense a change in relationship between two variable pressures and open or close a single electrical circuit by means of one snap action electrical switch. These types of switches are in fluid contact with a pressure container and in electrical communication with a pump. The pressure sensing element in a pressure switch is a diaphragm, a bourdon tube, a sealed piston, or some similar mechanism.
Float elements which float on liquid fluids have been used in such applications as to indicate the level of a liquid in a container, to open or close valves, and to start electric pumps. In these applications, when the float element rises to a specified level, it communicates that information by electrical or mechanical means to an indicator, valve or switching element where such element acts on the information according to a preprogrammed plan. Although a single float element is useful to initiate valve action or to start an electrical pump, a second sensing mechanism has been required to reverse the valve action or to stop the electrical pump. As a result, control mechanisms using float elements either accomplish a limited function as just described or are part of a quite complex and expensive mechanism.